Imaging systems that employ a drum to scan an imaging media past a writing head are well known in the art. Commonly the imaging head does not have enough imaging beams to write the entire width of the drum in a single rotation and hence the writing head is translated in a direction aligned with the drum axis to address the entire surface of the media.
It is important, particularly in high resolution imaging systems, to provide accurate and consistent rotation of the drum load to achieve acceptable imaging results. As an example, in Computer to Plate imaging systems, where a printing plate precursor is imaged by a laser based exposure head, a commonly used resolution is 2400 dpi. A common drum format used in such systems is a 32-inch circumference and 44-inch wide drum made from cast aluminium. Speed regulation of around 0.5% has found to be sufficient for imaging at these high resolutions. Furthermore, good positional control may also be required for loading and unloading imaging media in a system wherein media handling is automated.
A rotational drive system for an imaging drum will commonly employ servo control means to ensure that the drum rotates at a consistent speed. Such servo systems are well known in the art.
A problem arises in recently emerging imaging systems that have facilities for changing the drum during normal operation. One such system is the ThermoFlex® imaging system sold by Creo Inc. of Burnaby, BC, Canada. The ThermoFlex® system is presently being upgraded with the capability of imaging on a drum or on a sleeve. A sleeve is simply a media that is supplied attached to a tubular substrate rather than the more conventional flat plate format. To accommodate differing sleeve diameters, a variety of different sized drums are provided. In practice, a drum shell of the correct diameter is loaded onto a common mandrel in order to support a particular sleeve.
Whenever the drum load is changed the control parameters for the rotational drive system must also be changed since these parameters are typically set for a specific load and may not work with the new load. This is an inconvenience for the user and there remains a need for a method to easily accommodate the change between different drum loads.